1. Field of the Invention
The invention pertains to the field of active rectifiers. More particularly, the invention pertains to an active rectifier with an active centerpoint power bus balancing system.
2. Description of Related Art
Many types of three phase AC to DC active rectifiers are in use today. These systems convert three phase AC inputs to a DC output, while controlling the input current waveforms so as to maintain a high power factor, which reduces the cost of electrical power.
Some of the most efficient (most cost effective) active rectifiers utilize a three voltage level output. The output is split between two series connected capacitors. This capacitor centerpoint is needed as a return for power semiconductors, and its voltage must be kept centered between the two capacitors in order for efficient system operation, as well as to maintain low voltage stress on the power semiconductors.
A number of control schemes exist for maintaining centerpoint balance, but all have their limitations. Most will not work well under lightly loaded conditions, and will not maintain voltage balance when one capacitor load is much higher than the other capacitor load.
Every active rectifier system contains a housekeeping power supply, which is used to operate its control and power circuits.